MULTIPHOTON INTERFERENCE EFFECTS AT A BEAM SPLITTER

We investigate the photon statistics at the outputs of a four-port bea m splitter, when a strong coherent field is incident on one input port and various other fields enter at the second inner port. Some non-cla ssical interference effects are encountered. In particular, there is a large difference between the cases when a one photon field enters at input port 2 and when a field in a coherent state with an average of o ne photon enters at port 2. In the former case the probability P(m/1) of the difference m between the detected photons at output ports 3 and 4 has a minimum at m = 0 whenever the quantum efficiency exceeds one third. As the quantum efficiency falls from one to zero, the form of t he probability distribution P(m/1) changes drastically.